Feedstock Pretreatment, Pulping & Hydrolysis, Stock Preparation and Recycling

Laboratory and Pilot-scale Processes

Wood chipsMechanical Pretreatment of Feedstocks
Mechanical pretreatment of feedstocks is normally the first step in feedstock processing.  At Herty, we have a range of unique pilot-scale equipment that can be used to mechanically pre-treat biomass, such as wood chips, annual fibers, perennial, and purpose-grown energy crops. Herty has expertise and capabilities for feedstock drying, size-reduction and fiberizing that can produce ready-to-go feedstocks of specific moisture content, particle size and other key physical properties.

For pulping and fiberizing, Herty’s high-shear pulping equipment can be used to process difficult feedstocks such as cotton, hemp, flax, leather and synthetic fibers. Our high-shear pulper has a 2,000 gallon (7,571 liter) batch capacity and its rugged design is ideal for recovering valuable fibrous materials from products considered impossible to defiber such as electrical insulation papers, gasket stock, map paper, shoeboard, flooring base, and high wet strength papers. By recovering fiber, waste is reduced thus reducing disposal costs. Fiber recovered here can be used in conjunction with Herty’s refiners and papermachines to develop finished rolls for customer evaluations.

Wood chips: Hardwood and Softwood
Annual crops: Corn and Wheat Stover
Perennial crops: Miscanthus, Switch Grass 
Pretreatment Options                                                                            Wood chips: Hardwood and Softwood
Annual crops: Corn and Wheat Stover
Perennial crops: Miscanthus, Switch Grass


pulper headPulping and Hydrolysis
Herty is internationally-recognized as a leader in pulping process technology and in the chemical hydrolysis of biomass. During our 75-year history, Herty scientists and engineers have gained experience in the chemical pulping of virtually all fibrous materials and use this experience to support our clients and development partners achieve their goals.

In chemical pulping, cellulose is extracted from wood by dissolving the lignin that binds the cellulose fibers together. Herty supports all commercially-relevant pulping processes, including kraft, sulfite, neutral sulfite semichemical (NSSC), and soda pulping. In the pulping process, wood chips or other forms of biomass are subjected to chemical treatment at elevated temperatures and pressures. We have the ability to process biomass over a range of scale. Our laboratory reactors or digesters can process kg-scale amounts of biomass, which is ideal for exploratory research or process optimization. Our digesters are fully automated and instrumented, with H-factor control. In our pilot plant, our large 90 cu. foot (2.5 cu. meter) digester can process several tons per day, which can provide sufficient quantities of material for down-stream processing including papermaking trials.

At Herty, we support your process work with our capabilities for pulp characterization, including chemical and physical property analysis. We have extensive hand-sheet capabilities and lab testing services. Our three pilot papermachines can then be used to turn your pulp into a final product for end-use testing and market evaluation.

Wood chips: Hardwood and Softwood
Annual crops: Corn and Wheat Stover
Perennial crops: Miscanthus, Switch Grass 
0.3 cu.ft. rotary
0.8 cu.ft. batch
90 cu.ft. batch 
- Additive pulping
– Supporting equipment
– Fiber and chip characterization
– Chemical analysis


Screening is a key process in pulp and paper production. Screening enhances the quality of pulp by removing contaminants. Screening also allows pulps to be fractionated into long fiber and fines fractions. Fractionated pulps can then be used to optimize overall fiber development as well as the end-use properties of products. For example, increasing fines content in the final product can be used to improve surface smoothness and reduce porosity. Whereas increasing the long fiber fraction can increase product strength.

In pulp processing and stock preparation, Herty’s screening and fractionation systems allow larger quantities of pulp to be processed with realistic, scaleable operating conditions. Screens can run in a stand-alone manner or as an integral part of a stock preparation system. Our screening capabilities can be used for a number of different types of projects, including separation of fine and coarse fibers, in recycling operations to remove inks, and in process modification and evaluations to improve surface printability. Herty can evaluate screen designs and process conditions to help you select the right screening system for your applications. Through our fractionation and fiber characterization capabilities, Herty can also help you understand the potential of your fiber type and its most suitable commercial applications.

Screening Types
Pressurized screens
Holed and slotted screens
Operating Conditions
Consistency: 0.5-4 wt%
Capacity: 20-150 tons per day
Fiber Analysis
Fiber length distribution
Fiber coarseness


Rotor screensPilot Refining
Refining of pulp is used to modify pulp properties and optimize their end-use performance. In the refining process, the fiber is subjected to repetitive external stress, which promotes fibrillation and compliance. In pulp processing and stock preparation, Herty’s extensive range of refining system options allows large quantities of pulp to be processed under realistic operating conditions. Herty has considerable practical experience in optimizing the refining of pulps and reject refining, at both low and high consistencies.


Refiner Types
Single disk
Double disk

Operating Conditions
Lab scale: lbs per day
Calibrated Valley Beater and PFI mill
Pilot scale: Up to 20 tons per day
Process improvement
Product optimization
New fiber evaluation